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Most of the mountain ranges have been formed due to major changes that have taken place in the earths crust over the ages. They are classified in four categories on the basis of the process of their formation. The four categories are Fold Mountains, Block Mountains, Residual Mountains and Volcanic Mountains.
Fold Mountains are made up of many layers or rocks. They are formed due to violent contraction and pressure inside the earth. Because of this, the rocks turn wavy and overlap each other and their layers get folded to rise above the earth’s surface to form mountains. The Himalayas, the Andes, the Rockies and the Alps came into existence as a result of folding process.
Mountains formed by vertical faults are called block mountains. Great blocks of rock are uplifted above the surrounding terrain because of vertical movements along faults. The mountains rise as great tilted blocks. The Vosges in France and black forests in Germany are the example of Block Mountains.
Residual mountains are formed due to denudation and erosion by which high plateaus are gradually shaped into peaks and ridges. Denudation and erosion is caused by natural agents such as wind, water, snow, etc. the Catskill range in the southern New York state is an example of residual mountains. The Grand Canyon in Arizona, USA is the result of erosion by Colorado.
Volcanic mountains are formed due to the accumulating and solidification of lava, ash and debris erupted from the earth’s interior. They are basically cone shaped with a crater at the top. The Fujiyama in Japan is an example of volcanic mountains. (See volcanoes) Hood and Rainier of America are also example of such mountains ranges. The height of the mountains increases only a few millimeters every year.